The invention relates generally to electrical machines and in particular, to high torque density electrical machines.
Electrical machines, such as motors and generators are typically capable of delivering high torque and power at high speeds. However, certain applications require high torque and power at low speeds. Generally, electrical machines that deliver higher torque at lower speeds are expensive. Alternatively, a high torque at low speeds may be achieved by incorporating mechanical gearing for speed reduction. However, certain undesirable factors such as additional cost, acoustic noise, and mechanical wear and tear lead to a need for continuous lubrication and maintenance of such mechanical equipment.
Magnetic gears offer significant benefits as compared to their mechanical counterparts. These benefits include accurate position control on a drive shaft, higher torque at very low speed, and a lack of physical contact between an input shaft and an output shaft, to name only a few. However magnetic gearing is of a relatively complex design, and provides relatively low torque density.
More recently, planetary-like magnetic gear arrangements using rare-earth permanent magnets have been proposed, which result in favorable torque transmission capabilities between an inner rotor and an outer rotor. However, such systems require additional stationary windings resulting in a complex construction.
Therefore, it is desirable to provide a high torque density electrical machine that addresses the aforementioned issues.